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LTM8055
36VIN, 8.5A Buck-Boost
µModule Regulator
Features
Description
Complete Buck-Boost Switch Mode Power Supply
n V
OUT Equal, Greater, Less Than VIN
n Wide Input Voltage Range: 5V to 36V
n12V/3A Output from 6V
IN
n12V/6A Output from 12V
IN
n12V/8.5A Output from 24V
IN
n Up to 97.5% Efficient
n Adjustable Input and Output Average Current Limits
n Input and Output Current Monitors
n Parallelable for Increased Output Current
n Wide Output Voltage Range: 1.2V to 36V
n Selectable Switching Frequency: 100kHz to 800kHz
n Synchronization from 200kHz to 700kHz
n15mm × 15mm × 4.92mm BGA Package
The LTM ®8055 is a 36V IN, buck-boost µModule ®
(micromodule) regulator. Included in the package are the
switching controller, power switches, inductor and support
components. A resistor to set the switching frequency, a
resistor divider to set the output voltage, and input and
output capacitors are all that are needed to complete the
design. Other features such as input and output average
current regulation may be implemented with just a few
components. The LTM8055 operates over an input voltage range of 5V to 36V, and can regulate output voltages
between 1.2V and 36V. The SYNC input and CLKOUT
output allow easy synchronization.
n
Applications
n
n
n
n
High Power Battery-Operated Devices
Industrial Control
Solar Powered Voltage Regulator
Solar Powered Battery Charging
The LTM8055 is housed in a compact overmolded ball
grid array (BGA) package suitable for automated assembly
by standard surface mount equipment. The LTM8055 is
RoHS compliant.
L, LT, LTC, LTM, Linear Technology, the Linear logo, µModule and Burst Mode are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
Typical Application
Maximum Output Current and
Efficiency vs VIN
12VOUT from 5VIN to 36VIN Buck-Boost Regulator
LTM8055
SVIN
IIN
36.5k
600kHz
RUN
CTL
SS
SYNC
COMP
RT LL MODE
VOUT
12V
IOUT
GND
CLKOUT
IINMON
IOUTMON
FB
EFFICIENCY
22µF
25V
11.0k
96
8
68µF
100k
98
OUTPUT
CURRENT
6
94
92
90
4
EFFICIENCY (%)
4.7µF
50V
×2
10
VOUT
OUTPUT CURRENT (A)
VIN
VIN
5V TO 36V
88
2
86
8055 TA01a
0
0
10
20
VIN (V)
30
40
84
8055 TA01b
8055f
For more information www.linear.com/LTM8055
1
LTM8055
Absolute Maximum Ratings
Pin Configuration
(Note 1)
VIN, SVIN, VOUT, RUN, IIN, IOUT Voltage......................40V
FB, SYNC, CTL, MODE Voltage....................................6V
IINMON, IOUTMON Voltage..............................................6V
LL Voltage..................................................................15V
Maximum Junction Temperature (Notes 2, 3)........ 125°C
Storage Temperature.............................. –55°C to 125°C
Peak Solder Reflow Body Temperature.................. 245°C
TOP VIEW
SVIN
BANK 3
VIN
11
10
BANK 1
GND
IIN
9
8
7
6
5
BANK 2
VOUT
4
RUN
3
IINMON
2
IOUTMON
1
GND
A
B
C
D
IOUT
E
F G H J
K
L
LL
RT FB SS
CLKOUT
MODE SYNC
CTL
COMP
BGA PACKAGE
121-LEAD (15mm × 15mm × 4.92mm)
TJMAX = 125°C, θJA = 17.1°C/W, θJCbottom = 7.8°C/W, θJCtop = 17.5°C/W, θJB = 7.1°C/W,
WEIGHT = 2.8g, θ VALUES DETERMINED PER JEDEC JESD51-9, 51-12
Order Information
PART NUMBER
TERMINAL FINISH
PART MARKING*
DEVICE
FINISH CODE
PACKAGE
TYPE
MSL
RATING
TEMPERATURE RANGE
(SEE NOTE 2)
LTM8055EY#PBF
SAC305 (RoHS)
LTM8055Y
e1
BGA
3
–40°C to 125°C
LTM8055IY#PBF
SAC305 (RoHS)
LTM8055Y
e1
BGA
3
–40°C to 125°C
LTM8055IY
SnPb(63/37)
LTM8055Y
e0
BGA
3
–40°C to 125°C
LTM8055MPY#PBF
SAC305 (RoHS)
LTM8055Y
e1
BGA
3
–55°C to 125°C
LTM8055MPY
SnPb(63/37)
LTM8055Y
e0
BGA
3
–55°C to 125°C
Consult Marketing for parts specified with wider operating temperature
ranges. *Device temperature grade is indicated by a label on the shipping
container. Pad or ball finish code is per IPC/JEDEC J-STD-609.
• Recommended LGA and BGA PCB Assembly and Manufacturing
Procedures:
www.linear.com/umodule/pcbassembly
• Terminal Finish Part Marking:
www.linear.com/leadfree
• LGA and BGA Package and Tray Drawings:
www.linear.com/packaging
8055f
2
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LTM8055
Electrical Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. RUN = 1.5V unless otherwise noted. (Note 2)
PARAMETER
Minimum Input Voltage
Output DC Voltage
Output DC Current
Quiescent Current Into VIN (Tied to SVIN)
Output Voltage Line Regulation
Output Voltage Load Regulation
Output RMS Voltage Ripple
Switching Frequency
CONDITIONS
VIN = SVIN
FB = VOUT Through 100k
RFB = 100k/3.40k
VIN = 6V, VOUT = 12V
VIN = 24V, VOUT = 12V
RUN = 0.3V (Disabled)
No Load, MODE = 0.3V (DCM)
No Load, MODE = 1.5V (FCM)
5V < VIN < 36V, IOUT = 1A
VIN = 12V, 0.1A < IOUT < 6A
VIN = 12V, IOUT = 3A
RT = 453k
RT = 24.9k
MIN
1.2
36
3
8.5
0.1
8
45
0.5
0.5
25
100
800
Voltage at FB Pin
l
RUN Falling Threshold
RUN Hysteresis
RUN Low Threshold
RUN Pin Current
IIN Bias Current
Input Current Sense Threshold (IIN-VIN)
IOUT Bias Current
Output Current Sense Threshold (VOUT-IOUT)
LTM8055 Stops Switching
LTM8055 Starts Switching
LTM8055 Disabled
RUN = 1V
RUN = 1.6V
l
1.188
1.176
1.15
MAX
5.0
1
30
100
1.212
1.220
1.25
25
2
3
0.3
5
100
90
l
44
56
20
VCTL = Open
l
IINMON Voltage
IOUTMON Voltage
CTL Input Bias Current
SS Pin Current
CLKOUT Output High
CLKOUT Output Low
SYNC Input Low Threshold
SYNC Input High Threshold
SYNC Bias Current
MODE Input Low Threshold
MODE Input High Threshold
TYP
l
LTM8055 in Input Current Limit
LTM8055 in Output Current Limit
VCTL = 0V
VSS = 0V
10k to GND
10k to 5V
54.5
53
0.96
1.14
61.5
63
1.04
1.26
22
35
4
0.7
0.3
1.5
SYNC = 1V
11
0.3
1.5
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTM8055E is guaranteed to meet performance specifications
from 0°C to 125°C internal. Specifications over the full –40°C to
125°C internal operating temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTM8055I is guaranteed to meet specifications over the full –40°C
to 125°C internal operating temperature range. The LTM8055MP is
guaranteed to meet specifications over the full –55°C to 125°C internal
UNITS
V
V
V
A
A
µA
mA
mA
%
%
mV
kHz
kHz
V
V
V
mV
V
µA
nA
µA
mV
µA
mV
mV
V
V
µA
µA
V
V
V
V
µA
V
V
operating temperature range. Note that the maximum internal temperature
is determined by specific operating conditions in conjunction with board
layout, the rated package thermal resistance and other environmental
factors.
Note 3: The LTM8055 contains overtemperature protection that is
intended to protect the device during momentary overload conditions. The
internal temperature exceeds the maximum operating junction temperature
when the overtemperature protection is active. Continuous operation
above the specified maximum operating junction temperature may impair
device reliability.
8055f
For more information www.linear.com/LTM8055
3
LTM8055
Typical Performance Characteristics
Efficiency vs Output Current
(3.3VOUT)
100
0
2
4
6
8
OUTPUT CURRENT (A)
60
40
5VIN
12VIN
24VIN
36VIN
20
20
10
0
2
4
6
8
OUTPUT CURRENT (A)
100
40
Efficiency vs Output Current
(18VOUT)
3
6
OUTPUT CURRENT (A)
20
9
Efficiency vs Output Current
(36VOUT)
EFFICIENCY (%)
0
2
4
6
OUTPUT CURRENT (A)
5VIN
12VIN
24VIN
36VIN
50
0
1
2
3
4
OUTPUT CURRENT (A)
8055 G07
0
1
2
3
4
5
OUTPUT CURRENT (A)
10
5VIN
12VIN
24VIN
36VIN
5
7
5VIN
12VIN
24VIN
36VIN
8
4
3
2
0
6
Input Current vs Output Current
(5VOUT)
6
4
2
1
5
5VIN
12VIN
24VIN
36VIN
8055 G06
INPUT CURRENT (A)
INPUT CURRENT (A)
60
20
8
Input Current vs Output Current
(3.3VOUT)
6
70
10
60
40
5VIN
12VIN
24VIN
36VIN
7
80
4
6
8
OUTPUT CURRENT (A)
Efficiency vs Output Current
(24VOUT)
8055 G05
90
EFFICIENCY (%)
100
60
8055 G04
100
2
80
40
5VIN
12VIN
24VIN
36VIN
0
0
8055 G03
80
EFFICIENCY (%)
EFFICIENCY (%)
80
40
20
10
5VIN
12VIN
24VIN
36VIN
8055 G02
100
60
60
40
5VIN
12VIN
24VIN
36VIN
8055 G01
Efficiency vs Output Current
(12VOUT)
Efficiency vs Output Current
(8VOUT)
80
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
40
20
100
80
60
0
Efficiency vs Output Current
(5VOUT)
100
80
TA = 25°C, unless otherwise noted.
0
2
4
6
8
OUTPUT CURRENT (A)
10
8055 G08
0
0
2
4
6
8
OUTPUT CURRENT (A)
10
8055 G09
8055f
4
For more information www.linear.com/LTM8055
LTM8055
Typical Performance Characteristics
10
6
4
6
4
2
4
6
8
OUTPUT CURRENT (A)
0
10
0
3
6
OUTPUT CURRENT (A)
Input Current vs Output Current
(24VOUT)
4
6
5
4
3
5VIN
12VIN
24VIN
36VIN
1
2
4
OUTPUT CURRENT (A)
0
6
0
1
2
3
4
OUTPUT CURRENT (A)
8055 G13
10
100
8
80
6
4
12VOUT
18VOUT
24VOUT
36VOUT
2
0
0
10
20
VIN (V)
30
40
8055 G16
8
6
4
5
3.3VOUT
5VOUT
8VOUT
0
10
20
VIN (V)
8055 G14
TEMPERATURE RISE (°C)
OUTPUT CURRENT (A)
Maximum Output Current vs VIN
Maximum Output Current vs VIN
10
2
0
8
8055 G12
7
2
0
2
4
6
OUTPUT CURRENT (A)
8
INPUT CURRENT (A)
INPUT CURRENT (A)
6
0
Input Current vs Output Current
(36VOUT)
9
5VIN
12VIN
24VIN
36VIN
8
5VIN
12VIN
24VIN
36VIN
8055 G11
8055 G10
10
4
0
9
OUTPUT CURRENT (A)
0
6
2
Temperature Rise vs Output
Current (3.3VOUT)
100
5VIN
12VIN
24VIN
36VIN
60
40
20
0
0
2
4
6
8
OUTPUT CURRENT (A)
30
40
8055 G15
Temperature Rise vs Output
Current (5VOUT)
TEMPERATURE RISE (°C)
0
8
2
2
Input Current vs Output Current
(18VOUT)
10
5VIN
12VIN
24VIN
36VIN
8
INPUT CURRENT (A)
INPUT CURRENT (A)
10
5VIN
12VIN
24VIN
36VIN
8
Input Current vs Output Current
(12VOUT)
INPUT CURRENT (A)
Input Current vs Output Current
(8VOUT)
TA = 25°C, unless otherwise noted.
10
8055 G17
5VIN
12VIN
24VIN
36VIN
80
60
40
20
0
0
2
4
6
8
OUTPUT CURRENT (A)
10
8055 G18
8055f
For more information www.linear.com/LTM8055
5
LTM8055
Typical Performance Characteristics
Temperature Rise vs Output
Current (8VOUT)
TA = 25°C, unless otherwise noted.
Temperature Rise vs Output
Current (12VOUT)
Temperature Rise vs Output
Current (18VOUT)
80
80
80
60
40
5VIN
12VIN
24VIN
36VIN
20
0
0
2
4
6
8
OUTPUT CURRENT (A)
60
40
5VIN
12VIN
24VIN
36VIN
20
0
10
0
2
4
6
OUTPUT CURRENT (A)
8055 G19
40
0
8
40
5VIN
12VIN
24VIN
36VIN
20
0
2
4
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
60
0
2
4
6
OUTPUT CURRENT (A)
6
Output Voltage Ripple, Unmodified
DC2017A Demo Board 12VOUT
24VIN
6A LOAD
(BUCK)
100mV/DIV
80
MEASURED WITH HP461N
150MHz AMPLIFIER
12VIN
6A LOAD
(BUCK-BOOST)
100mV/DIV
60
40
6VIN
3A LOAD
(BOOST)
100mV/DIV
5VIN
12VIN
24VIN
36VIN
20
0
8
8055 G21
100
80
5VIN
12VIN
24VIN
36VIN
20
Temperature Rise vs Output
Current (36VOUT)
100
TEMPERATURE RISE (°C)
60
8055 G20
Temperature Rise vs Output
Current (24VOUT)
0
TEMPERATURE RISE (°C)
100
TEMPERATURE RISE (°C)
100
TEMPERATURE RISE (°C)
100
0
8055 G22
1
2
3
4
OUTPUT CURRENT (A)
0.5µs/DIV
5
8055 G24
8055 G23
Maximum Output Current vs
CTL Voltage, Unmodified
DC2017A, 12VIN
Start-Up Behavior, DC2017A,
24VIN, 3A Resistive Load
8
NO CSS
OUTPUT CURRENT (A)
2V/DIV
7
CSS = 0.022µF
CSS = 0.22µF
6
5
4
3
2
1
500µs/DIV
8055 G25
0
0
0.2
0.4 0.6 0.8
1
CTL VOLTAGE (V)
1.2
1.4
8055 G26
8055f
6
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LTM8055
Pin Functions
GND (Bank 1, Pin L1): Tie these GND pins to a local ground
plane below the LTM8055 and the circuit components.
In most applications, the bulk of the heat flow out of the
LTM8055 is through these pads, so the printed circuit
design has a large impact on the thermal performance of
the part. See the PCB Layout and Thermal Considerations
sections for more details. Return the RFB1/RFB2 feedback
divider to this net.
MODE (Pin G2): Switching Mode Input. The LTM8055 operates in forced continuous mode when MODE is open, and
can operate in discontinuous switching mode when MODE
is low. In discontinuous switching mode, the LTM8055
will block reverse inductor current. This pin is normally
left open or tied to LL. This pin may be tied to GND for the
purpose of blocking reverse current if no output current
sense resistor is used.
VOUT (Bank 2): Power Output Pins. Apply output filter
capacitors between these pins and GND pins.
RT (Pin H1): Timing Resistor. The RT pin is used to program
the switching frequency of the LTM8055 by connecting a
resistor from this pin to ground. The range of oscillation is
100kHz to 800kHz. The Applications Information section of
the data sheet includes a table to determine the resistance
value based on the desired switching frequency. Minimize
capacitance at this pin.
VIN (Bank 3): Input Power. The VIN pin supplies current to
the LTM8055’s internal power switches and to one terminal
of the optional input current sense resistor. This pin must
be locally bypassed with an external, low ESR capacitor;
see Table 1 for recommended values.
IOUT (Pin D1): Output Current Sense. Tie this pin to the
output current sense resistor. The output average current
sense threshold is 58mV, so the LTM8055 will regulate
the output current to 58mV/RSENSE, where RSENSE is the
value of the output current sense resistor in ohms. The
load is powered through the sense resistor connected at
this pin. Tie this pin to VOUT if no output current sense
resistor is used. Keep this pin within ±0.5V of VOUT under
all conditions.
SYNC (Pin H2): External Synchronization Input. The SYNC
pin has an internal pull-down resistor. See the Synchronization section in Applications Information for details. Tie
this pin to GND when not used.
LL (Pin F1): Light Load Indicator. This pin indicates that
the output current, as sensed through the resistor connected between VOUT and IOUT, is approximately equivalent
to 10mV or less. Its state is meaningful only if a current
sense resistor is applied between VOUT and IOUT. This is
useful to change the switching behavior of the LTM8055
in light load conditions.
COMP (Pin J2): Compensation Pin. The LTM8055 is
equipped with internal compensation that works well with
most applications. In some cases, the performance of the
LTM8055 can be enhanced by modifying the control loop
compensation by applying a capacitor or RC network to
this pin.
SVIN (Pins F10, F11): Controller Power Input. Apply a
separate voltage above 5V if the LTM8055 is required to
operate when the main power input (VIN) is below 5V.
Bypass these pins with a high quality, low ESR capacitor.
If a separate supply is not used, connect these pins to VIN.
CLKOUT (Pin G1): Clock Output. Use this pin as a clock
source when synchronizing other devices to the switching frequency of the LTM8055. When this function is not
used, leave this pin open.
FB (Pin J1): Output Voltage Feedback. The LTM8055
regulates the FB pin to 1.2V. Connect the FB pin to a
resistive divider between the output and GND to set the
output voltage. See Table 1 for recommended FB divider
resistor values.
SS (Pin K1): Soft-Start. Connect a capacitor from this pin
to GND to increase the soft-start time. Soft-start reduces
the input power source’s surge current by gradually increasing the controller’s current limit. Larger values of the
soft-start capacitor result in longer soft-start times. If no
soft-start is required, leave this pin open.
CTL (Pin K2): Current Sense Adjustment. Apply a voltage
below 1.2V to reduce the current limit threshold of IOUT.
Drive CTL to less than 50mV to stop switching. The CTL
pin has an internal pull-up resistor to 2V. If not used,
leave open.
8055f
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7
LTM8055
Pin Functions
IOUTMON (Pin L2): Output Current Monitor. This pin produces a voltage that is proportional to the voltage between
VOUT and IOUT. IOUTMON will equal 1.2V when VOUT – IOUT
= 58mV. This feature is generally useful only if a current
sense resistor is applied between VOUT and IOUT.
IINMON (Pin L3): Input Current Monitor. This pin produces
a voltage that is proportional to the voltage between IIN
and VIN. IINMON will equal 1V when IIN – VIN = 50mV. This
feature is generally useful only if a current sense resistor
is applied between VIN and IIN.
RUN (Pin L4): LTM8055 Enable. Raise the RUN pin voltage
above 1.2V for normal operation. Above 1.2V (typical), but
below 6V, the RUN pin input bias current is less than 1μA.
Below 1.2V and above 0.3V, the RUN pin sinks 3μA so
the user can define the hysteresis with the external resistor selection. This will also reset the soft-start function.
If RUN is 0.3V or less, the LTM8055 is disabled and the
SVIN quiescent current is below 1μA.
IIN (Pin L9): Input Current Sense. Tie this pin to the input
current sense resistor. The input average current sense
threshold is 50mV, so the LTM8055 will regulate the input
current to 50mV/RSENSE, where RSENSE is the value of the
input current sense resistor in ohms. Tie to VIN when not
used. Keep this pin within ±0.5V of VIN under all conditions.
Block Diagram
VIN
VOUT
SVIN
IOUT
4.7µH
IIN
0.47µF
50V
0.2µF
RUN
GND
2V
SS
100k
FB
100k
CLKOUT
BUCK-BOOST CONTROLLER
0.1µF
IINMON
IOUTMON
CTL
MODE
COMP
LL
RT
SYNC
8055 BD
8055f
8
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LTM8055
Operation
The LTM8055 is a standalone nonisolated buck-boost
switching DC/DC power supply. The buck-boost topology allows the LTM8055 to regulate its output voltage for
input voltages both above and below the magnitude of the
output. The maximum output current depends upon the
input voltage. Higher input voltages yield higher maximum
output current.
This converter provides a precisely regulated output voltage programmable via an external resistor divider from
1.2V to 36V. The input voltage range is 5V to 36V, but the
LTM8055 may be operated at lower input voltages if SVIN
is powered by a voltage source above 5V. A simplified
block diagram is given on the previous page.
The LTM8055 contains a current mode controller, power
switching elements, power inductor and a modest amount
of input and output capacitance. The LTM8055 is a fixed
frequency PWM regulator. The switching frequency is set
by connecting the appropriate resistor value from the RT
pin to GND.
The output voltage of the LTM8055 is set by connecting
the FB pin to a resistor divider between VOUT and GND.
In addition to regulating its output voltage, the LTM8055
is equipped with average current control loops for both the
input and output. Add a current sense resistor between IIN
and VIN to limit the input current below some maximum
value. The IINMON pin reflects the current flowing though
the sense resistor between IIN and VIN.
A current sense resistor between VOUT and IOUT allows
the LTM8055 to accurately regulate its output current to
a maximum value set by the value of the sense resistor.
When the resistor is present, the IOUTMON pin reflects the
output current flowing through VOUT.
In general, the LTM8055 should be used with an output
sense resistor to limit the maximum output current, as
buck-boost regulators are capable of delivering large
currents when the output voltage is lower than the input,
if demanded.
Furthermore, while the LTM8055 does not require an
output sense resistor to operate, it uses information from
the sense resistor to optimize its performance. If an output sense resistor is not used, the efficiency or output
ripple may degrade, especially if the current through the
integrated inductor is discontinuous. In some cases, an
output sense resistor is required to adequately protect the
LTM8055 against output overload or short-circuit.
A voltage less than 1.2V applied to the CTL pin reduces
the maximum output current. Drive CTL to about 50mV
to stop switching. The current flowing through the sense
resistor is reflected by the output voltage of the IOUTMON pin.
Driving the SYNC pin will synchronize the LTM8055 to an
external clock source. The CLKOUT pin sources a signal
that is the same frequency but approximately 180° out of
phase with the internal oscillator.
If more output current is required than a single LTM8055
can provide, multiple devices may be operated in parallel.
Refer to the Parallel Operation section of Applications
Information for more details.
An internal regulator provides power to the control circuitry
and the gate driver to the power MOSFETs. This internal
regulator draws power from the SVIN pin. The RUN pin is
used to place the LTM8055 in shutdown, disconnecting
the output and reducing the input current to less than 1μA.
The LTM8055 is equipped with a thermal shutdown that
inhibits power switching at high junction temperatures.
The activation threshold of this function is above 125°C
to avoid interfering with normal operation, so prolonged
or repetitive operation under a condition in which the
thermal shutdown activates may damage or impair the
reliability of the device.
8055f
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9
LTM8055
Applications Information
For most applications, the design process is straight forward, summarized as follows:
1. Look at Table 1 and find the row that has the desired
input range and output voltage.
2. Apply the recommended CIN, COUT, RFB1/RFB2 and RT
values.
3. Apply the output sense resistor to set the output current
limit. The output current is limited to 58mV/RSENSE,
where RSENSE is the value of the output current sense
resistor in ohms.
While these component combinations have been tested for
proper operation, it is incumbent upon the user to verify
proper operation over the intended system’s line, load and
environmental conditions. Bear in mind that the maximum
output current is limited by junction temperature, the relationship between the input and output voltage magnitude
and other factors. Please refer to the graphs in the Typical
Performance Characteristics section for guidance.
The maximum frequency (and attendant RT value) at
which the LTM8055 should be allowed to switch is given
in Table 1 in the fMAX column, while the recommended
frequency (and RT value) for optimal efficiency over the
given input condition is given in the fOPTIMAL column.
There are additional conditions that must be satisfied if
the synchronization function is used. Please refer to the
Synchronization section for details.
Note that Table 1 calls out both ceramic and electrolytic
output capacitors. Both of the capacitors called out in
the table must be applied to the output. The electrolytic
capacitors in Table 1 are described by voltage rating,
value and ESR. The voltage rating of the capacitor may
be increased if the application requires a higher voltage
stress derating. The LTM8055 can tolerate variation
in the ESR; other capacitors with different ESR may
be used, but the user must verify proper operation
over line, load and environmental conditions. Table 2
gives the description and part numbers of electrolytic
capacitors used in the LTM8055 development testing and
design validation.
Table 1. Recommended Component Values and Configuration (TA = 25°C)
VIN RANGE
5V to 24V
VOUT
CIN
COUT
RFB1/RFB2 fOPTIMAL (kHz) RT(OPTIMAL) fMAX (kHz) RT(MAX)
3.3V 2 × 4.7µF, 50V, X5R, 0805 22µF, 6.3V, X5R, 0805
100k/56.2k
600
36.5k
800
24.9k
100µF, 6V, 75mΩ, Electrolytic
5V to 28V
5V 2 × 4.7µF, 50V, X5R, 0805 22µF, 6.3V, X5R, 0805
100k/31.6k
550
39.2k
800
24.9k
100µF, 6V, 75mΩ, Electrolytic
5V to 31V
8V 2 × 4.7µF, 50V, X5R, 0805 47µF, 10V, X5R, 1206
100k/17.4k
500
45.3k
800
24.9k
100µF, 16V, 100mΩ, Electrolytic
5V to 36V
12V 2 × 4.7µF, 50V, X5R, 1210 22µF, 25V, X5R, 0805
100k/11k
600
36.5k
800
24.9k
68µF, 16V, 200mΩ, Electrolytic
5V to 36V
18V 2 × 4.7µF, 50V, X7R, 1210 2 x 22µF, 25V, X5R, 1210
100k/6.98k
500
45.3k
800
24.9k
47µF, 25V, 900mΩ, Electrolytic
5V to 36V
24V 2 × 4.7µF, 50V, X7R, 1210 22µF, 25V, X5R, 1210
100k/5.23k
650
31.6k
800
24.9k
33µF, 35V 300mΩ, Electrolytic
5.5V to 36V 36V 2 × 4.7µF, 50V, X7R, 1210 10µF, 50V, X5R, 1206
100k/3.40k
650
31.6k
800
24.9k
10µF, 50V 120mΩ, Electrolytic
Notes: An input bulk capacitor is required. The output capacitance uses a combination of a ceramic and electrolytic in parallel. Other combinations of
resistor values for the RFB network are acceptable.
Table 2. Electrolytic Caps Used in LTM8055 Testing
DESCRIPTION
100µF, 6V, 75mΩ, Tantalum C Case
100µF, 16V, 100mΩ, Tantalum Y Case
68µF, 16V, 200mΩ, Tantalum C Case
47µF, 25V, 900mΩ, Tantalum D Case
33µF, 35V, 300mΩ, Tantalum D Case
10µF, 50V, 120mΩ, Aluminum 6.3 × 6mm case
MANUFACTURER
AVX
AVX
AVX
AVX
AVX
Suncon
PART NUMBER
TPSC107M006R0075
TPSY107M016R0100
TPSC686M016R0200
TAJD476M025R
TPSD336M035R0300
50HVP10M
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Applications Information
Capacitor Selection Considerations
Table 3. Switching Frequency vs RT Value
The CIN and COUT capacitor values in Table 1 are the
minimum recommended values for the associated operating conditions. Applying capacitor values below those
indicated in Table 1 is not recommended, and may result
in undesirable operation. Using larger values is generally
acceptable, and can yield improved dynamic response, if
it is necessary. Again, it is incumbent upon the user to
verify proper operation over the intended system’s line,
load and environmental conditions.
Ceramic capacitors are small, robust and have very low
ESR. However, not all ceramic capacitors are suitable.
X5R and X7R types are stable over temperature and applied voltage and give dependable service. Other types,
including Y5V and Z5U have very large temperature and
voltage coefficients of capacitance. In an application circuit they may have only a small fraction of their nominal
capacitance resulting in much higher output voltage ripple
than expected.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LTM8055. A
ceramic input capacitor combined with trace or cable
inductance forms a high Q (underdamped) tank circuit.
If the LTM8055 circuit is plugged into a live supply, the
input voltage can ring to twice its nominal value, possibly exceeding the device’s rating. This situation is easily
avoided; see the Hot-Plugging Safely section.
Frequency Selection
The LTM8055 uses a constant frequency PWM architecture that can be programmed to switch from 100kHz to
800kHz by tying a resistor from the RT pin to ground.
Table 3 provides a list of RT resistor values and their resultant frequencies.
FREQUENCY
RT VALUE (kΩ)
100
453
200
147
300
84.5
400
59
500
45.3
600
36.5
700
29.4
800
24.9
An external resistor from RT to GND is required. Do not
leave this pin open, even when synchronizing to an external clock. When synchronizing the switching of the
LTM8055 to an external signal source, the frequency range
is 200kHz to 700kHz.
Operating Frequency Trade-Offs
It is recommended that the user apply the optimal RT
value given in Table 1 for the input and output operating
condition. System level or other considerations, however,
may necessitate another operating frequency. While the
LTM8055 is flexible enough to accommodate a wide range
of operating frequencies, a haphazardly chosen one may
result in undesirable operation under certain operating or
fault conditions. A frequency that is too high can reduce
efficiency, generate excessive heat or even damage the
LTM8055 if the output is overloaded or short circuited.
A frequency that is too low can result in a final design
that has too much output ripple, too large of an output
capacitor or is unstable.
Parallel Operation
Two or more LTM8055s may be combined to provide
increased output current by configuring them as a master and a slave, as shown in Figure 1. Each LTM8055 is
equipped with an IOUTMON and a CTL pin. The IOUTMON
pin’s 0 to 1.2V signal reflects the current passing through
the output sense resistor, while a voltage less than 1.2V
applied to the CTL pin will limit the current passing through
the output sense resistor. By applying the voltage of the
master’s IOUTMON pin to the slave’s CTL pin, the two units
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LTM8055
Applications Information
will source the same current to the load, assuming each
LTM8055 output current sense resistor is the same value.
MASTER
OUTPUT CURRENT
SENSE RESISTOR
TO LOAD
VOUT
IOUT
IOUTMON
UNITY GAIN
BUFFER
Paralleled LTM8055s should normally be allowed to switch
in discontinuous mode to prevent current from flowing
from the output of one unit into another; that is, the
MODE pin should be tied to LL. In some cases, operating
the master in forced continuous (MODE open) and the
slaves in discontinuous mode (MODE = LL) is desirable.
If so, current from the output can flow into the master’s
input. Please refer to Input Precaution in this section for
a discussion of this behavior.
Minimum Input Voltage and RUN
CTL
SLAVE
VOUT
OUTPUT CURRENT
SENSE RESISTOR
IOUT
8055 F01
Figure 1. Two or More LTM8055s May Be Connected in a
Master/Slave Configuration for Increased Output Current
The design of a master-slave configuration is straight
forward:
1.Apply the FB resistor network to the master, choosing
the proper values for the desired output voltage. Suggested values for popular output voltages are provided
in Table 1.
2.Apply a FB resistor network to the individual slaves
so that the resulting output is higher than the desired
output voltage.
3.Apply the appropriate output current sense resistors
between VOUT and IOUT. If the same value is used for the
master and slave units, they will share current equally.
The LTM8055 needs a minimum of 5V for proper operation, but system parameters may dictate that the device
operate only above some higher input voltage. For example, a LTM8055 may be used to produce 12VOUT, but
the input power source may not be budgeted to provide
enough current if the input supply voltage is below 8V.
The RUN pin has a typical falling voltage threshold of
1.2V and a typical hysteresis of 25mV. In addition, the
pin sinks 3µA below the RUN threshold. Based upon the
above information and the circuit shown in Figure 2, the
VIN rising (turn-on) threshold is:
VIN = ( 3µA •R1) +1.225V
and the VIN falling turn-off threshold is:
VIN = 1.2
R1+R2
R2
LTM8055
VIN
4.Connect the master IOUTMON to the slaves’ CTL pin
through a unity gain buffer. The unity gain buffer is
required to isolate the output impedance of the LTM8055
from the integrated pull-up on the CTL pins.
5.Tie the outputs together.
Note that this configuration does not require the inputs to
be tied together, making it simple to power a single heavy
load from multiple input sources. Ensure that each input
power source has sufficient voltage and current sourcing
capability to provide the necessary power. Please refer
to the Maximum Output Current vs VIN and Input Current
vs Output Current curves in the Typical Performance
Characteristics section for guidance.
R1+R2
R2
R1
RUN
R2
8055 F02
Figure 2. This Simple Resistor Network Sets the Minimum
Operating Input Voltage Threshold with Hysteresis
Minimum Input Voltage and SVIN
The minimum input voltage of the LTM8055 is 5V, but this
is only if VIN and SVIN are tied to the same voltage source.
If SVIN is powered from a power source at or above 5VDC,
VIN can be allowed to fall below 5V and the LTM8055 can
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LTM8055
Applications Information
still operate properly. Some examples of this are provided
in the Typical Applications section.
Soft-Start
Soft-start reduces the input power sources’ surge currents
by gradually increasing the controller’s current. As indicated
in the Block Diagram, the LTM8055 has an internal softstart RC network. Depending upon the load and operating
conditions, the internal network may be sufficient for the
application. To increase the soft-start time, simply add a
capacitor from SS to GND.
Output Current Limit (IOUT)
The LTM8055 features an accurate average output current
limit set by an external sense resistor placed between VOUT
and IOUT as shown in Figure 3. VOUT and IOUT internally
connect to a differential amplifier that limits the current
when the voltage VOUT-IOUT reaches 58mV. The current
limit is:
IOUT(LIM) =
58mV
RSENSE
where RSENSE is the value of the sense resistor in ohms.
Most applications should use an output sense resistor as
shown in Figure 3, if practical. The internal buck-boost
power stage is current limited, but is nonetheless capable
of delivering large amounts of current in an overload
condition, especially when the output voltage is much
lower than the input and the power stage is operating as
a buck converter.
LTM8055
VOUT
IOUT
tying the LL and MODE pins together can improve performance—see Switching Mode in this section.
In high step-down voltage regulator applications, the
internal current limit can be quite high to allow proper
operation. This can potentially damage the LTM8055
in overload or short-circuit conditions. Apply an output
current sense resistor to set an appropriate current limit
to protect the LTM8055 against these fault conditions.
Output Current Limit Control (CTL)
Use the CTL input to reduce the output current limit from
the value set by the external sense resistor applied between
VOUT and IOUT. The typical control range is between 0V
and 1.2V. The CTL pin does not directly affect the input
current limit. If this function is not used, leave CTL open.
Drive CTL to less than about 50mV to stop switching. The
CTL pin has an internal pull-up resistor to 2V.
Input Current Limit (IIN)
Some applications require that LTM8055 draw no more
than some predetermined current from the power source.
Current limited power sources and power sharing are two
examples. The LTM8055 features an accurate input current
limit set by an external sense resistor placed between IIN
and VIN as shown in Figure 4. VIN and IIN internally connect
to a differential amplifier that limits the current when the
voltage IIN-VIN reaches 50mV. The current limit is:
IIN(LIM) =
50mV
RSENSE
where RSENSE is the value of the sense resistor in ohms.
If input current limiting is not required, simply tie IIN to VIN.
RSENSE
LOAD
POWER
SOURCE
8055 F03
Figure 3. Set The LTM8055 Output Current Limit with an External
Sense Resistor
RSENSE
LTM8055
VIN
IIN
8055 F04
When the voltage across the output sense resistor falls
to about 1/10th of full scale, the LL pin pulls low. If there
is no output sense resistor, and IOUT is tied to VOUT, LL
will be active low. Applying an output sense resistor and
Figure 4. Set the LTM8055 Input Current Limit with an
External Sense Resistor
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LTM8055
Applications Information
Input Current Monitor (IINMON)
The IINMON pin produces a voltage equal to approximately
20 times the voltage of IIN – VIN. Since the LTM8055 input
current limit engages when IIN – VIN = 50mV, IINMON will
be 1V at maximum input current.
Output Current Monitor (IOUTMON)
The IOUTMON pin produces a voltage proportional to the
voltage of VOUT – IOUT. Since the LTM8055 output current
limit engages when VOUT – IOUT = 58mV, IOUTMON will be
1.2V at maximum output current.
Synchronization
The LTM8055 switching frequency can be synchronized to
an external clock using the SYNC pin. Driving SYNC with
a 50% duty cycle waveform is a good choice, otherwise
maintain the duty cycle between about 10% and 90%. When
synchronizing, a valid resistor value (that is, a value that
results in a free-running frequency of 100kHz to 800kHz)
must be connected from RT to GND.
While an RT resistor is required for proper operation, the
value of this resistor is independent of the frequency of
the externally applied SYNC signal. Be aware, however,
that the LTM8055 will switch at the frequency prescribed
by the RT value if the SYNC signal terminates, so choose
an appropriate resistor value.
CLKOUT
The CLKOUT signal reflects the internal switching clock of
the LTM8055. It is phase shifted by approximately 180° with
respect to the leading edge of the internal clock. If CLKOUT
is connected to the SYNC input of another LTM8055, the
two devices will switch about 180° out of phase.
Input Precaution
In applications where the output voltage is deliberately
pulled up above the set regulation voltage or the FB pin is
abruptly driven to a new voltage, the LTM8055 may attempt
to regulate the voltage by removing energy from the load
for a short period of time after the output is pulled up.
Since the LTM8055 is a synchronous switching converter,
it delivers this energy to the input. If there is nothing on the
LTM8055 input to consume this energy, the input voltage
may rise. If the input voltage rises without intervention, it
may rise above the absolute maximum rating, damaging
the part. Carefully examine the input voltage behavior to
see if the application causes it to rise.
In many cases, the system load on the LTM8055 input
bus will be sufficient to absorb the energy delivered by the
μModule regulator. The power required by other devices
will consume more than enough to make up for what
the LTM8055 delivers. In cases where the LTM8055 is
the largest or only power converter, this may not be true
and some means may need to be devised to prevent the
LTM8055’s input from rising too high. Figure 5a shows a
passive crowbar circuit that will dissipate energy during
momentary input overvoltage conditions. The break-down
voltage of the Zener diode is chosen in conjunction with
the resistor R to set the circuit’s trip point. The trip point
is typically set well above the maximum VIN voltage under
normal operating conditions. This circuit does not have
a precision threshold, and is subject to both part-to-part
and temperature variations, so it is most suitable for applications where the maximum input voltage is much less
than the 40VIN absolute maximum. As stated earlier, this
type of circuit is best suited for momentary overvoltages.
Figure 5a is a crowbar circuit, which attempts to prevent
the input voltage from rising above some level by dumping
energy to GND through a power device. In some cases,
it is possible to simply turn off the LTM8055 when the
input voltage exceeds some threshold. An example of this
circuit is shown in Figure 5b. When the power source on
the output drives VIN above a predetermined threshold,
the comparator pulls down on the RUN pin and stops
switching in the LTM8055. When this happens, the input
capacitance needs to absorb the energy stored within the
LTM8055’s internal inductor, resulting in an additional
voltage rise. This voltage rise depends upon the input
capacitor size and how much current is flowing from the
LTM8055 output to input.
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Applications Information
LOAD
CURRENT
VIN
ZENER
DIODE
Q
VOUT
LTM8055
GND
SOURCING
LOAD
R
8055 F05a
Figure 5a. The MOSFET Q Dissipates Momentary Energy to
GND. The Zener Diode and Resistor Are Chosen to Ensure That
the MOSFET Turns On Above the Maximum VIN Voltage Under
Normal Operation
LOAD
CURRENT
VIN
VOUT
LTM8055
RUN
10µF
–
+
GND
SOURCING
LOAD
EXTERNAL
REFERENCE
VOLTAGE
buck, buck-boost or boost operating modes, especially at
lighter loads. In such a case, it can be desirable to operate in forced continuous mode except when the internal
inductor current is about to reverse. If so, apply a current
sense resistor between VOUT and IOUT and tie the LL and
MODE pins together. The LL pin is low when the current
through the output sense resistor is about one-tenth the
full-scale maximum. When the output current falls to this
level, the LL pin will pull the MODE pin down, putting the
LTM8055 in discontinuous mode, preventing reverse current from flowing from the output to the input. In the case
where MODE and LL are tied together, a small capacitor
(~0.1µF) from these pins to GND may improve the light
load transient response by delaying the transition from
the discontinuous to forced continuous switching modes.
MODE may be tied to GND for the purpose of blocking
reverse current if no output current sense resistor is used.
FB Resistor Divider and Load Regulation
8055 F05b
Figure 5b. This Comparator Circuit Turns Off the LTM8055 if
the Input Rises Above a Predetermined Threshold. When the
LTM8055 Turns Off, the Energy Stored in the Internal Inductor
Will Raise VIN a Small Amount Above the Threshold
Switching Mode
The MODE pin allows the user to select either discontinuous
mode or forced continuous mode switching operation. In
forced continuous mode, the LTM8055 will not skip cycles,
even when the internal inductor current falls to zero or even
reverses direction. This has the advantage of operating at
the same fixed frequency for all load conditions, which can
be useful when designing to EMI or output noise specifications. Forced continuous mode, however, uses more
current at light loads, and allows current to flow from the
load back into the input if the output is raised above the
regulation point. This reverse current can raise the input
voltage and be hazardous if the input is allowed to rise
uncontrollably. Please refer to Input Precautions in this
section for a discussion of this behavior.
Forced continuous operation may provide improved
output regulation when the LTM8055 transitions from
The LTM8055 regulates its FB pin to 1.2V, using a resistor
divider to sense the output voltage. The location at which
the output voltage is sensed affects the load regulation.
If there is a current sense resistor between VOUT and
IOUT, and the output is sensed at VOUT, the voltage at the
load will drop by the value of the current sense resistor
multiplied by the output current. If the output voltage can
be sensed at IOUT, the load regulation may be improved.
PCB Layout
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8055. The LTM8055 is nevertheless a switching power supply, and care must be taken to
minimize EMI and ensure proper operation. Even with the
high level of integration, you may fail to achieve specified
operation with a haphazard or poor layout. See Figure 6
for a suggested layout. Ensure that the grounding and
heat sinking are acceptable.
A few rules to keep in mind are:
1.Place the RFB and RT resistors as close as possible to
their respective pins.
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LTM8055
Applications Information
2.Place the CIN capacitor as close as possible to the VIN
and GND connection of the LTM8055.
board. Pay attention to the location and density of the
thermal vias in Figure 6. The LTM8055 can benefit from
the heat sinking afforded by vias that connect to internal
GND planes at these locations, due to their proximity
to internal power handling components. The optimum
number of thermal vias depends upon the printed
circuit board design. For example, a board might use
very small via holes. It should employ more thermal
vias than a board that uses larger holes.
3.Place the COUT capacitor as close as possible to the
VOUT and GND connection of the LTM8055.
4.Minimize the trace resistance between the optional
output current sense resistor, ROUT, and VOUT. Minimize
the loop area of the IOUT trace and the trace from VOUT
to ROUT.
5.Minimize the trace resistance between the optional input
current sense resistor, RIN and VIN. Minimize the loop
area of the IIN trace and the trace from VIN to RIN.
6.Place the CIN and COUT capacitors such that their
ground current flow directly adjacent or underneath
the LTM8055.
7.Connect all of the GND connections to as large a copper
pour or plane area as possible on the top layer. Avoid
breaking the ground connection between the external
components and the LTM8055.
8.Use vias to connect the GND copper area to the board’s
internal ground planes. Liberally distribute these GND
vias to provide both a good ground connection and
thermal path to the internal planes of the printed circuit
Hot-Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LTM8055. However, these capacitors
can cause problems if the LTM8055 is plugged into a live
supply (see Linear Technology Application Note 88 for a
complete discussion). The low loss ceramic capacitor
combined with stray inductance in series with the power
source forms an underdamped tank circuit, and the voltage at the VIN pin of the LTM8055 can ring to more than
twice the nominal input voltage, possibly exceeding the
LTM8055’s rating and damaging the part. If the input supply
is poorly controlled or the LTM8055 is hot-plugged into an
energized supply, the input network should be designed
CIN
GND
SVIN
VIN
GND/THERMAL VIAS
RIN
INPUT
SENSE
IIN
COUT
INPUT
RUN
VOUT SIGNAL VIA
VOUT
MODE SYNC
IOUT
IOUT
LL
RT
FB
ROUT
OUTPUT
SENSE
GND
VOUT SIGNAL VIA
8055 F06
Figure 6. Layout Showing Suggested External Components,
GND Plane and Thermal Vias
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LTM8055
Applications Information
to prevent this overshoot. This can be accomplished by
installing a small resistor in series with VIN, but the most
popular method of controlling input voltage overshoot is
to add an electrolytic bulk capacitor to the VIN net. This
capacitor’s relatively high equivalent series resistance
damps the circuit and eliminates the voltage overshoot.
The extra capacitor improves low frequency ripple filtering and can slightly improve the efficiency of the circuit,
though it is likely to be the largest component in the circuit.
Thermal Considerations
The LTM8055 output current may need to be derated if
it is required to operate in a high ambient temperature or
deliver a large amount of continuous power. The amount
of current derating is dependent upon the input voltage,
output power and ambient temperature. The temperature
rise curves given in the Typical Performance Characteristics section can be used as a guide. These curves were
generated by a LTM8055 mounted to a 58cm2 4-layer FR4
printed circuit board. Boards of other sizes and layer count
can exhibit different thermal behavior, so it is incumbent
upon the user to verify proper operation over the intended
system’s line, load and environmental operating conditions.
The thermal resistance numbers listed in the Pin Configuration of the data sheet are based on modeling the µModule
package mounted on a test board specified per JESD 51-9
(Test Boards for Area Array Surface Mount Package Thermal
Measurements). The thermal coefficients provided on this
page are based on JESD 51-12 (Guidelines for Reporting
and Using Electronic Package Thermal Information).
For increased accuracy and fidelity to the actual application,
many designers use FEA to predict thermal performance.
To that end, the Pin Configuration of the data sheet typically gives four thermal coefficients:
θJA – Thermal resistance from junction to ambient.
θJCbottom – Thermal resistance from junction to the bottom
of the product case.
θJCtop – Thermal resistance from junction to top of the
product case.
While the meaning of each of these coefficients may seem
to be intuitive, JEDEC has defined each to avoid confusion
and inconsistency. These definitions are given in JESD
51-12, and are quoted or paraphrased below:
θJA is the natural convection junction-to-ambient air
thermal resistance measured in a one cubic foot sealed
enclosure. This environment is sometimes referred to as
“still air” although natural convection causes the air to
move. This value is determined with the part mounted to
a JESD 51-9 defined test board, which does not reflect an
actual application or viable operating condition.
θJCbottom is the thermal resistance between the junction
and bottom of the package with all of the component power
dissipation flowing through the bottom of the package. In
the typical µModule converter, the bulk of the heat flows
out the bottom of the package, but there is always heat
flow out into the ambient environment. As a result, this
thermal resistance value may be useful for comparing
packages but the test conditions don’t generally match
the user’s application.
θJCtop is determined with nearly all of the component power
dissipation flowing through the top of the package. As the
electrical connections of the typical µModule converter are
on the bottom of the package, it is rare for an application
to operate such that most of the heat flows from the junction to the top of the part. As in the case of θJCbottom, this
value may be useful for comparing packages but the test
conditions don’t generally match the user’s application.
θJB is the junction-to-board thermal resistance where
almost all of the heat flows through the bottom of the
µModule converter and into the board, and is really the
sum of the θJCbottom and the thermal resistance of the
bottom of the part through the solder joints and through a
portion of the board. The board temperature is measured
a specified distance from the package, using a 2-sided,
2-layer board. This board is described in JESD 51-9.
Given these definitions, it should now be apparent that none
of these thermal coefficients reflects an actual physical
operating condition of a µModule converter. Thus, none
θJB – Thermal resistance from junction to the printed
circuit board.
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LTM8055
Applications Information
JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)
CASE (TOP)-TO-AMBIENT
RESISTANCE
JUNCTION-TO-CASE (TOP)
RESISTANCE
JUNCTION
JUNCTION-TO-BOARD RESISTANCE
AMBIENT
JUNCTION-TO-CASE
CASE (BOTTOM)-TO-BOARD
(BOTTOM) RESISTANCE
RESISTANCE
BOARD-TO-AMBIENT
RESISTANCE
8055 F07
µMODULE CONVERTER
Figure 7
of them can be individually used to accurately predict the
thermal performance of the product. Likewise, it would
be inappropriate to attempt to use any one coefficient to
correlate to the junction temperature versus load graphs
given in the product’s data sheet. The only appropriate way
to use the coefficients is when running a detailed thermal
analysis, such as FEA, which considers all of the thermal
resistances simultaneously.
A graphical representation of these thermal resistances
is given in Figure 7.
The die temperature of the LTM8055 must be lower than
the maximum rating of 125°C, so care should be taken in
the layout of the circuit to ensure good heat sinking of the
LTM8055. The bulk of the heat flow out of the LTM8055
is through the bottom of the μModule converter and the
BGA pads into the printed circuit board. Consequently a
poor printed circuit board design can cause excessive
heating, resulting in impaired performance or reliability.
Please refer to the PCB Layout section for printed circuit
board design suggestions.
The blue resistances are contained within the µModule
converter, and the green are outside.
8055f
18
For more information www.linear.com/LTM8055
LTM8055
Typical Applications
12VOUT Fan Power from 3VIN to 36VIN with Analog
Current Control and 2A Input Current Limiting
Maximum Output Current
vs CTL Voltage
1µF
50V
0.022Ω
VIN
SVIN
LTM8055
VOUT
36.5k
600kHz
GND
CLKOUT
IINMON
IOUTMON
FB
22µF
25V
+
FAN
68µF
25V
11.0k
8055 TA02a
0.2V TO 1.2V
CONTROL RANGE
0.8
0.6
0.4
0.2
0
FAN CONTROL
DAC
12VIN
1.0
100k
RUN
COMP
SS
SYNC
CTL
RT LL MODE
1.2
VOUT
12V MAX
IOUT
IIN
10µF
50V
0.05Ω
OUTPUT CURRENT (A)
VIN
3V TO 36V
0
0.2
0.4
0.6
0.8
CTL VOLTAGE (V)
1
1.2
8055 TA02b
24VOUT from 7VIN to 36VIN with 2.1A Accurate Current Limit
Output Voltage vs Output Current
VIN
VIN
7V TO 36V
LTM8055
VOUT
0.027Ω
IOUT
SVIN
25
VOUT
24V
12VIN
IIN
36.5k
600kHz
RUN
COMP
SS
SYNC
CTL
RT
LL MODE
100k
GND
CLKOUT
IINMON
IOUTMON
FB
22µF
25V
+
33µF
35V
5.23k
8055 TA03a
OUTPUT VOLTAGE (V)
10µF
50V
20
15
10
5
0
0
0.5
1
1.5
2
OUTPUT CURRENT (A)
2.5
8055 TA03b
8055f
For more information www.linear.com/LTM8055
19
LTM8055
Typical Applications
3.3VOUT from 9VIN to 24VIN with 5A Accurate Current Limit and
Output Current Monitor
Output Voltage vs Output Current
VIN
VIN
9V TO 24V
4.0
0.011Ω
VOUT
LTM8055
VOUT
3.3V
IOUT
SVIN
3.5
10µF
50V
36.5k
600kHz
RUN
CTL
SS
SYNC
COMP
RT
LL
100k
MODE
GND
CLKOUT
IINMON
IOUTMON
FB
22µF
6.3V
OUTPUT
CURRENT
MONITOR
56.2k
+
OUTPUT VOLTAGE (V)
IIN
100µF
6.3V
8055 TA04a
3.0
2.5
2.0
1.5
1.0
0.5
0
0
1
2
3
4
OUTPUT CURRENT (A)
5
6
8055 TA04b
Two LTM8055s Paralleled to Get More Output Current. The Two µModules Are
Synchronized and Switching 180° Out Of Phase
VIN
VIN
7V TO 36V
SVIN
LTM8055
(MASTER)
VOUT
0.008Ω
IOUT
IOUTMON Voltage vs Output Current
for Each Channel, 12VIN
VOUT
12V
IIN
47pF
IINMON
IOUTMON
FB
22µF
25V
100k
+
11k
GND
+
1.0
68µF
25V
LT1636
VIOUTMON (V)
36.5k
600kHz
1.2
RUN
CTL
SS
SYNC
COMP
RT
CLKOUT
LL MODE
–
10µF
50V
0.8
0.6
0.4
0.2
VIN
SVIN
LTM8055
(SLAVE)
VOUT
0.008Ω
0
IOUT
IIN
10µF
50V
36.5k
600kHz
47pF
RUN
COMP
SS
SYNC
RT
LL MODE
GND
CTL
CLKOUT
IINMON
IOUTMON
FB
MASTER
SLAVE
22µF
25V
+
0
5
10
15
COMBINED CURRENTS OF BOTH CHANNELS (A)
8055 TA05b
68µF
25V
100k
9.31k
8055 TA05a
8055f
20
For more information www.linear.com/LTM8055
LTM8055
Typical Applications
Two LTM8055s Powered from Different Input Sources to Run a Single Load. Each LTM8055 Draws No More Than 1.8A from Its
Respective Power Source, and Are Synchronized 180° Out Of Phase with Each Other
0.025Ω
SUPPLY 1
6V TO 36VIN
VIN
LTM8055
SVIN
IOUT
IIN
10µF
50V
36.5k
600kHz
RUN
CTL
SS
SYNC
COMP
RT
CLKOUT
LL MODE
47pF
0.025Ω
SUPPLY 2
6V TO 36VIN
VIN
VOUT
IINMON
IOUTMON
FB
11k
VOUT
IOUT
SVIN
IIN
10µF
50V
100k
RUN
CTL
SS
SYNC
COMP
RT
LL MODE
47pF
22µF
25V
GND
CLKOUT
IINMON
IOUTMON
FB
11k
8055 TA06a
Input Current and Output Voltage vs
Output Current 12VIN
14
2.5
12
2.0
10
1.5
8
6
1.0
0.5
0
0
VOUT (V)
INPUT CURRENT (A)
36.5k
600kHz
68µF
35V
100k
GND
LTM8055
+
22µF
25V
3A MAX
VOUT
12V
4
VOUT
INPUT CURRENT,
REGULATOR 1 2
INPUT CURRENT,
REGULATOR 2 0
1
2
3
4
OUTPUT CURRENT (A)
8055 TA06b
8055f
For more information www.linear.com/LTM8055
21
LTM8055
Package Description
Table 4. LTM8055 Pin Assignment (Arranged by Pin Number)
PIN ID
FUNCTION
PIN ID
FUNCTION
PIN ID
FUNCTION
PIN ID
FUNCTION
PIN ID
FUNCTION
PIN ID
FUNCTION
A1
VOUT
B1
VOUT
C1
VOUT
D1
IOUT
E1
GND
F1
LL
A2
VOUT
B2
VOUT
C2
VOUT
D2
GND
E2
GND
F2
GND
A3
VOUT
B3
VOUT
C3
VOUT
D3
GND
E3
GND
F3
GND
A4
VOUT
B4
VOUT
C4
VOUT
D4
GND
E4
GND
F4
GND
A5
VOUT
B5
VOUT
C5
VOUT
D5
GND
E5
GND
F5
GND
A6
VOUT
B6
VOUT
C6
VOUT
D6
GND
E6
GND
F6
GND
A7
GND
B7
GND
C7
GND
D7
GND
E7
GND
F7
GND
A8
GND
B8
GND
C8
GND
D8
GND
E8
GND
F8
GND
A9
GND
B9
GND
C9
GND
D9
GND
E9
GND
F9
GND
A10
GND
B10
GND
C10
GND
D10
GND
E10
GND
F10
SVIN
A11
GND
B11
GND
C11
GND
D11
GND
E11
GND
F11
SVIN
PIN ID
FUNCTION
PIN ID
FUNCTION
PIN ID
FUNCTION
PIN ID
FUNCTION
PIN ID
FUNCTION
G1
CLKOUT
H1
RT
J1
FB
K1
SS
L1
GND
G2
MODE
H2
SYNC
J2
COMP
K2
CTL
L2
IOUTMON
G3
GND
H3
GND
J3
GND
K3
GND
L3
IINMON
G4
GND
H4
GND
J4
GND
K4
GND
L4
RUN
G5
GND
H5
GND
J5
GND
K5
GND
L5
GND
G6
GND
H6
GND
J6
GND
K6
GND
L6
GND
G7
GND
H7
GND
J7
GND
K7
GND
L7
GND
G8
GND
H8
GND
J8
GND
K8
GND
L8
GND
G9
GND
H9
GND
J9
GND
K9
GND
L9
IIN
G10
VIN
H10
VIN
J10
VIN
K10
VIN
L10
VIN
G11
VIN
H11
VIN
J11
VIN
K11
VIN
L11
VIN
Package Photo
8055f
22
For more information www.linear.com/LTM8055
0.635 ±0.025 Ø 121x
2.540
SUGGESTED PCB LAYOUT
TOP VIEW
1.270
PACKAGE TOP VIEW
0.3175
0.000
0.3175
4
1.270
PIN “A1”
CORNER
E
2.540
aaa Z
6.350
5.080
3.810
3.810
5.080
6.350
D
X
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
For more
information
www.linear.com/LTM8055
6.350
5.080
3.810
2.540
1.270
0.000
1.270
2.540
3.810
5.080
6.350
Y
aaa Z
// bbb Z
SYMBOL
A
A1
A2
b
b1
D
E
e
F
G
H1
H2
aaa
bbb
ccc
ddd
eee
H1
SUBSTRATE
A1
NOM
4.92
0.60
4.32
0.78
0.635
15.00
15.00
1.27
12.70
12.70
0.32
4.00
A
A2
MAX
5.12
0.70
4.42
0.85
0.660
NOTES
DETAIL B
PACKAGE SIDE VIEW
0.37
4.05
0.15
0.10
0.20
0.30
0.15
TOTAL NUMBER OF BALLS: 121
0.27
3.95
MIN
4.72
0.50
4.22
0.71
0.610
b1
DIMENSIONS
ddd M Z X Y
eee M Z
DETAIL A
Øb (121 PLACES)
DETAIL B
H2
MOLD
CAP
ccc Z
Z
(Reference LTC DWG# 05-08-1891 Rev A)
Z
BGA Package
121-Lead (15.00mm × 15.00mm × 4.92mm)
F
11
10
9
7
6
5
4
PACKAGE BOTTOM VIEW
8
G
3
2
1
DETAIL A
DETAILS OF PIN #1 IDENTIFIER ARE OPTIONAL,
BUT MUST BE LOCATED WITHIN THE ZONE INDICATED.
THE PIN #1 IDENTIFIER MAY BE EITHER A MOLD OR
MARKED FEATURE
4
L
K
J
H
G
F
E
D
C
B
A
7
TRAY PIN 1
BEVEL
!
PACKAGE IN TRAY LOADING ORIENTATION
LTMXXXXXX
µModule
7
SEE NOTES
PIN 1
BGA 121 1112 REV A
PACKAGE ROW AND COLUMN LABELING MAY VARY
AMONG µModule PRODUCTS. REVIEW EACH PACKAGE
LAYOUT CAREFULLY
6. SOLDER BALL COMPOSITION CAN BE 96.5% Sn/3.0% Ag/0.5% Cu
OR Sn Pb EUTECTIC
5. PRIMARY DATUM -Z- IS SEATING PLANE
BALL DESIGNATION PER JESD MS-028 AND JEP95
3
2. ALL DIMENSIONS ARE IN MILLIMETERS
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994
e
COMPONENT
PIN “A1”
b
3
SEE NOTES
LTM8055
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
8055f
23
LTM8055
Typical Application
14.4V, 3A Lead-Acid Battery Charger Input Current Limited to 2.1A
Input Current vs Input Voltage,
IOUT = 3A
2.5
1µF
50V
0.022Ω
VIN SVIN
0.02Ω
VOUT
LTM8055
IOUT
IIN
36.5k
600kHz
RUN
CTL
SS
SYNC
COMP
RT
LL MODE
GND
VOUT
14.4V
+
100k
10µF
50V
CLKOUT
IINMON
IOUTMON
FB
INPUT CURRENT (A)
2.0
VIN
3V TO 36V
47µF
25V
1.5
1.0
0.5
22µF
25V
9.09k
0
8055 TA07a
0
10
20
30
INPUT VOLTAGE (V)
40
8055 TA07b
Design Resources
SUBJECT
DESCRIPTION
µModule Design and Manufacturing Resources
Design:
• Selector Guides
• Demo Boards and Gerber Files
• Free Simulation Tools
µModule Regulator Products Search
1. Sort table of products by parameters and download the result as a spread sheet.
Manufacturing:
• Quick Start Guide/Demo Manual
• PCB Design, Assembly and Manufacturing Guidelines
• Package and Board Level Reliability
2. Search using the Quick Power Search parametric table.
TechClip Videos
Quick videos detailing how to bench test electrical and thermal performance of µModule products.
Digital Power System Management
Linear Technology’s family of digital power supply management ICs are highly integrated solutions that
offer essential functions, including power supply monitoring, supervision, margining and sequencing,
and feature EEPROM for storing user configurations and fault logging.
Related Parts
PART NUMBER DESCRIPTION
COMMENTS
LTM4605
Higher Power Buck-Boost (Up to 60W)
External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT
≤ 16V
LTM4607
Higher Power Buck-Boost (Up to 60W)
External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT
≤ 24V
LTM4609
Higher Power Buck-Boost (Up to 60W)
External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT
≤ 34V
LTM8045
Smaller, Lower Power
SEPIC and Inverting; 700mA, 6.25mm × 11.25mm × 4.92mm BGA
LTM8046
Isolated, Lower Power
Flyback Topology, 550mA (5VOUT, 24VIN), UL60950, 2kVAC
8055f
24 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTM8055
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTM8055
LT 0215 • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2015